Adhesively bonded rail joint

ABSTRACT

Adhesively bonded rail joint which is quick to assemble and easy to dismantle and reassemble. The face of each joint bar of the rail joint has a layer of thermoplastic adhesive which upon moderate heating adheres strongly under moderate pressure to conforming surfaces of the rail ends. Because the thermoplastic adhesive does not cure, the joint bars are easily separated from the rails by reheating the adhesive and can be reapplied or used as part of a new rail joint.

This is a division of application Ser. No. 255,613 filed May 22, 1972now U.S. Pat. No. 3,837,948.

FIELD OF THE INVENTION

The present invention concerns rail joints, specifically adhesivelybonded rail joints, and is particularly concerned with electricallyinsulating rail joints.

BACKGROUND OF THE INVENTION

Railroad rails are commonly bolted together with a pair of fishplates orjoint bars in a manner allowing considerable vertical movement of therails relative to each other. As each train wheel leaves one rail, itdepresses that rail relative to the other and then batters the otherrail. After a time, it becomes necessary to repair the battered end ofthe rail or to replace the rail.

This problem has been partially overcome by welding the rails together,but welded track involves additional problems arising from hugeexpansion and contraction forces in long sections of welded track withchanges in temperature. Also, it is expensive to replace individualrails of welded track. At electrically insulated joints of welded track,the same problem of rail-end batter is involved.

In an effort to reduce rail end batter, some railroads have beenexperimenting with adhesively bonded rail joints in order to inhibitvertical movement of the rail ends with respect to each other. However,such adhesively bonded rail joints have created a new set of problems.Adhesives which have thus far been used cure rather slowly and requirethat the line be kept out of service for unduly long periods of time.Then the joint bars become so strongly bonded to the rail that the jointis difficult to dismantle if maintenance is required.

DESCRIPTION OF THE PRIOR ART

U.S. Pat. No. 3,100,080 (Fiechter) shows a rail joint wherein the jointbars are adhered to rail ends by a thermosetting resin composition,preferably an epoxy resin composition. Since the resin compositionextends over the whole area between the joint bars and the rail ends andalso surrounds the bolts and the space between the rail ends, this jointmight be electrically insulating, although the patent does not mentionthis.

U.S. Pat. No. 3,139,364 (Fiechter) discloses the same rail joint andadds disclosure showing how to make such a rail joint eitherelectrically conducting or insulating.

"Railway Age", June 14, 1971, pages 48-9, reports a number of fieldinstallations of adhesively bonded rail joints. See also "DerEisenbahningenieur", Vol. 13, No. 3, March 1962.

Orgotherm Inc. of Chicago has imported a "glued insulated rail joint"from Th. Goldschmidt A.G./ElectroThermit G.m.b.H., Essen, Germany. Inmaking this rail joint, a polyvinyl chloride paste is first applied onlyto the rail end faces and/or both sides of the end post, and two-part,coldsetting synthetic resin is then applied over the fishing surfaces.

THE PRESENT INVENTION

The present invention concerns an adhesively bonded rail joint whichprovides advantages of welded track while avoiding its primarydisadvantages and without introducing new disadvantages. Like a weldedjoint or an adhesively bonded rail joint of the prior art, the noveljoint effectively locks the rail ends together so that essentially norelative vertical movement is permitted, thus effectively inhibitingrail end batter. As compared to adhesively bonded rail joints of theprior art, the novel rail joint is more convenient to install (the trackcrew need not mix or spread the adhesive), is operational within ashorter period (no waiting period for the adhesive to become thermoset)and is easier to dismantle (because it employs a thermoplastic adhesivewhich does not cure). Upon dismantling by heating the rails, one or bothof the rails may be repaired or replaced and the joint remade withoutemploying additional materials (providing the adhesive is handled so asnot to become contaminated with foreign matter). Like the prioradhesively bonded joints, the novel rail joint may be electricallyinsulating and thus provide the insulated joints of an otherwise weldedtrack.

The rail joint of the present invention comprises a pair of joint bars,each of which has broad faces shaped to conform to broad surfaces of therails to be joined, including at least major portions of the surfacesunderlying the rail heads and of the upper surfaces of the rail bases inthe area of the rail joint. The broad faces of the joint bars carrythermoplastic adhesive layers, initially about 10-60 mils in thicknessand preferably 25-50 mils in thickness which should permit reasonabledimensional variations in the rails and joint bars. The adhesive ischaracterized by:

a. modulus in tension of at least 200,000 psi at all temperatures from-20°F to 120°F,

b. tensile strength (ASTM D 638-60T) of at least 2000 psi at alltemperatures from -20°F to 120°F,

c. sufficiently low softening point that it wets steel at less than500°F under moderate pressure, preferably at 350°F or below,

d. shear adhesion to cold rolled steel (ASTM D 1002-64) of at least 2000psi at all temperatures from -20°F to 120°F, and

e. water absorption of less than one percent, preferably less than 0.25percent, after 24-hour immersion.

Thermoplastic adhesives of various chemical classes have proved to beuseful, including Phenoxy-type polymers obtained by polymerizingequivalent amounts of bisphenol A [i.e., 2,2-(4-hydroxyphenyl)propane]and the diglycidyl ether of bisphenol A; polysulfone resins;amorphous-type polyesters such as Eastman Polyester GPRO(X11426);glass-fiber reinforced polypropylene such as "Profil" of Fiberfill, Inc.Ideally, the thermoplastic adhesive wets steel at 250°-300°F undermoderate pressure and provides shear adhesion to cold rolled steel andtensile strength of 3000-5000 psi. It has been found that this idealcombination of properties can be achieved using commercially availableadhesives only by adding modifiers to one of the above-identifiedadhesives. For example, this ideal combination of properties has beenachieved by modifying a Phenoxy-type polymer having an average molecularweight of 20,000-30,000 and a glass transition temperature of about100°C with any one of the following materials in amounts up to about tenpercent of the weight of the modified adhesive:

1. A lower molecular weight polymer of bisphenol A and the diglycidylether of bisphenol A having a Gardner-Holdt viscosity of Z₄ to Z₈.

2. polyglycidyl ether of bisphenol A having a Durrans' softening pointof 95°-105°C and an epoxide equivalent of 870-1025.

3. Heat polymerized wood rosin having a softening point of 82°C.

In order to improve adhesion, a thermosetting resin coating may be curedin situ between the joint bar and the layer of thermoplastic adhesive.If desired, the rail surfaces after being cleaned and heated may beprimed, for example, by spraying a thin coating of the samethermoplastic resin as on the joint bars, if desired including suitableanticorrosion, coupling and/or wetting agents. Because the thermoplasticadhesive does not cure, the joint bars of the novel rail joint can belater separated from the rails at any time by heating the rails abovethe softening point of the adhesive -- even if the rails were primedwith a thermosetting resin.

To assemble the novel rail joint, the rail ends may be preheated to atemperature at which the adhesive will wet steel under moderatepressure, after which the joint bars are positioned and fastened to therail ends, usually with bolts extending through aligned bores in thejoint bars and the rail webs. The heat from the rail ends causes theadhesive to flow under the pressure of the bolts, creating an adhesivebond that is sufficient for train operation as soon as the rails havecooled.

Because present rail joints require holes in the ends of the rails, itis convenient to employ bolts to assemble the novel rail joint. Aboltless joint may be assembled using ordinary C-clamps which may beremoved as soon as the rail ends have cooled. Preferably the C-clampsfit beneath the rails so that they can remain in place permanently,especially at curved sections of track or at any other locations atwhich the adhesive would be subjected to appreciable peel forces. Bymaintaining the adhesive under mechanical pressure through the jointbars, the adhesive is subjected primarily to shear forces.

Instead of bolts or clamps, one may employ any means suitable to applymoderate pressure to the thermoplastic adhesive, at least until theadhesive has cooled.

The novel rail joint may be made electrically insulating by employingelectrically insulating joint bars such as glass-filament-reinforcedresin of the type employed in U.S. Pat. No. 3,369,752. Preferably theseare fitted with four bearing plate means as illustrated in FIG. 1 or inFIG. 3 of said patent such that there is no electrically conducting pathfrom bolts in one rail to bolts in the other rail.

If desired, steel joint bars can be used in an electrically insulatingversion of the novel rail joint. To accomplish this, the adhesive (whichitself is normally electrically insulating) should cover the fishingsurfaces of the joint bars which are so shaped that they are safelyinsulated from the corresponding rail surfaces. Preferably, additionalelectrically insulating material such as resinimpregnated cloth isbonded over the fishing surfaces of the steel bars. If steel bolts areused with such a construction, they should be fitted with electricallyinsulating grommets. Because the adhesive bond effectively preventsmovement of the rail ends relative to the joint bars, such grommets aresubjected only to light forces.

In any electrically insulating rail joint, an electrically insulatingend post is preferably positioned between the rails, but this is of lessimportance in the present invention because the adhesive bond restrainsthe rails from moving relative to each other.

THE DRAWING

In the drawing:

FIG. 1 is a front elevation of a preferred embodiment of the rail jointof this invention;

FIG. 2 is an enlarged elevation, partly in section, taken generallyalong line 2--2 of FIG. 1; and

FIG. 3 is an elevation, partly in section, of another embodiment of therail joint of this invention.

The joint bars 10 shown in FIGS. 1 and 2 of the drawing are constructedin the same manner as are the joint bars illustrated in FIGS. 1 and 2 ofU.S. Pat. No. 3,369,752. Each joint bar is a laminate of a large numberof thin layers of aligned bundles of glass filaments embedded inthermoset resin. One such layer of each joint bar provides a flat outerface 11 against which a pair of cast iron bearing plates 12, 13 rest.Each of the bearing plates 12, 13 has a bore 14 aligned with each bore15 of the contiguous joint bar and each attaching hole 16 in the rails17, 18 through which bolts 19 extend.

The inner face 20 of each joint bar 10 is machined to match theunderlying surface 21 of each rail head, the surface 22 of each web andthe tapered surface 23 of each rail base. A slight depression 24(FIG. 1) is machined centrally in each joint bar 10 in order to provideclearance from the sharp corners at the ends of the rails 17, 18 whichmight otherwise cut into the joint bars under the weight of passingrailroad equipment. Prior to assembly, a uniform layer of thermoplasticadhesive 25 is applied to the face 20 of each joint bar.

A major portion of the glass filaments of each joint bar 10 extend inthe lengthwise direction of the joint bar, or if a substantial number ofthe filaments extend obliquely to the lengthwise direction, thelengthwise component of all of the filaments should exceed thetransverse component. To insure adequate transverse reinforcement, thetransverse component of all of the filaments preferably is at leastone-tenth of the lengthwise component, which transverse component may beprovided by a layer of transverse filaments every 100 mils or lessthrough the thickness of each joint bar.

Sandwiched between the rails 17, 18 is an insulating end post 26(FIG. 1) which may be formed of any durable, water-resistant,electrically insulating material in the shape of the rail cross-section.A laminate of layers of aligned bundles of glass filaments embedded inthermoset resin has been found to be particularly suitable.

To assemble the rail joint shown in FIGS. 1 and 2, the rail surfaces 21,22 and 23 are thoroughly cleaned and the rail is heated to above thetemperature at which the adhesive 25 wets steel under moderate pressure.The end post 26, joint bars 10 and bearing plates 12, 13 are thenpositioned, and the bolts 19 are tightened sufficiently to cause a bead27 of the adhesive 25 to form around the full periphery of each jointbar. As soon as the adhesive has cooled, the joint is fully operational.

DESCRIPTION OF A SECOND EMBODIMENT OF THE INVENTION

The rail joint illustrated in FIG. 3 is similar to that shown in FIGS. 1and 2 except that it employs a pair of steel angle bars 30 instead ofthe reinforced resin joint bars 10, each angle bar having two separatedinner faces, each of which has been provided with a thermoplasticadhesive layer 31, 32.

EXAMPLE 1

Laminated plastic joint bars were constructed from sheets cut from aroll which had been made by drawing through a heated bath of epoxy resinand hardener a web of lineally-aligned bundles of continuous glassfilaments, viz., 300 ends or bundles per inch of ECG 140's, 20 endroving, vinyl silane size. Each end included 204 glass monofilaments ofabout 0.00038-inch diameter. The epoxy resin was made fromepichlorhydrin and bisphenol A and had a Durrans' softening point ofapproximately 30°-40°C, and the hardener was basically isophthalyldihydrazide. After immersion in the bath of resin which was maintainedat about 95°C, the web of glass was passed through squeeze rolls todensify and flatten it to a glass:resin ratio of 64:36 by weight and wasthen contacted with a disposable low-adhesion liner and wound therewithinto roll form.

Eighty sheets cut from the web were stacked with 39 sheets cut from asecond web which was identical to the first except that it was madeusing only 200 bundles per inch of the glass filaments. Every thirdsheet of the stack was cut from the second web and was laid up with itsfilaments crosswise to the filaments of the sheets cut from the firstweb. The whole was placed in a heated platen press which had beenpreheated to 120°C. Pressure was gradually applied over a period of 8minutes to 50 psi to give a thickness of 1 9/16 inches. After two hoursin the press at 120°C, the cured panel was removed to an air-circulatingoven where it was post-cured for 16 hours at about 138°C. After beingcooled to room temperature, the panel was sawed and machined to providea pair of joint bars 10 as illustrated in FIGS. 1 and 2 of the drawing,each 36 inches in the direction of predominant filament reinforcementand about 5 inches in the direction of the crosswise filaments. Sixholes were drilled, each 1 1/8 inches in diameter.

Selected as the thermoplastic adhesive was a polymer of equivalentamounts of bisphenol A and the diglycidyl ether of bisphenol A having anaverage molecular weight within the approximate range of 20,000 to30,000 and a glass transition temperature of about 100°C. Such a polymeris commercially available from Union Carbide Corporation as "PhenoxyPAHJ". Two sheets of this adhesive of 30-40 mils thickness were shapedin a vacuum former at 120°C to conform approximately to the inner face20 of each joint bar 10.

Before applying the shaped adhesive sheets, an adhesion-promotingcoating was spread on each face 20 to a thickness of 10-20 mils. Thiscoating consisted essentially of a mixture of a liquid epoxy resin and aroom-temperature-reactive long-chain polyamine curing agent plus afiller comprising fifty percent by weight of the mixture. The epoxyresin was a polyglycidyl ether of bisphenol A having an epoxideequivalent of 175-210 and a little less than two 1,2-epoxy groups peraverage molecular weight. The filler comprised glass microspheres of50μm average diameter having an amino-silane finish to promote adhesionto epoxy resin.

The shaped thermoplastic adhesive sheet was progressively laid againstthe freshly applied adhesion-promoting coating so as not to entrap air,and sufficient pressure was applied in doing so to squeeze out abouthalf of the epoxy resin mixture. Each joint bar and adheredthermoplastic adhesive sheet was placed in an oven at 120°C for twohours to cure the epoxy resin mixture.

To join two rails, the rail ends were cleaned by sandblasting andattached to a rail puller to maintain a spacing between the rails ofabout one-half inch. The rails were heated with a gas-fired weldingtorch until their temperature reached 400°F as indicated by athermocouple held against the rail ends at several locations. The endpost, joint bars and bearing plates were positioned and the boltstorqued to an initial pressure of 1000 psi between the joint bars andrail ends, which pressure was sufficient to form a bead of resin aroundthe entire periphery of each joint bar. After cooling, the rail pullerwas removed and the joint was ready for service.

The rail joint of this example has been in service on a main line of arailroad in the United States for about 8 months. In spite of heavytraffic at speeds up to 35 miles per hour, there is no indication offailure. Three similar experimental installations have been in use forsomewhat shorter periods without failure.

We claim:
 1. Adhesively bonded rail joint which is quick to assemble andeasy to dismantle and reassemble comprising a pair of joint bars havingbroad faces shaped to conform to broad surfaces of the rails includingat least major portions of the surfaces underlying the rail heads andthe upper surfaces of the rail bases in the area of the rail joint, eachof said broad faces carrying a thermoplastic adhesive layer about 10-60mils in thickness and an adhesion-promoting coating of in-situ curedthermosetting resin between each thermoplastic adhesive layer and jointbar, which adhesive is characterized by:a. modulus in tension of atleast 200,000 psi at all temperatures from -20°F to 120°F, b. tensilestrength of at least 2000 psi at all temperatures from -20°F to 120°F,c. sufficiently low softening point that it wets steel at less than500°F under moderate pressure, d. shear adhesion to cold rolled steel ofat least 2000 psi at all temperatures from -20°F to 120°F, and e. waterabsorption of less than 1 percent after 24-hour immersion.
 2. Rail jointas defined in claim 1 wherein the joint bars and rails have alignedholes and there are bolts extending through the holes for application ofpressure insuring that the adhesive wets the rail surfaces when thejoint is assembled.
 3. Rail joint as defined in claim 2 wherein each ofsaid joint bars comprises fiber-reinforced resin, which rail joint iselectrically insulating.
 4. Rail joint as defined in claim 3 wherein thejoint bars have flat vertical outer faces, and four bearing plate meansrest against said faces in aligment with said holes to distribute thepressure from the bolts over substantially the full joint bars.
 5. Railjoint as defined in claim 2 wherein the joint bars are electricallyconductive, the thermoplastic adhesive is electrically insulating,additional electrically insulating material covers all fishing surfacesof the joint bars, and the shanks of the bolts are electricallyinsulated from the rails by electrical insulating grommets so that therail joint is electrically insulating.
 6. Rail joint as defined in claim2 wherein the joint bars are steel angle bars.
 7. Adhesively bonded railjoint which is quick to assemble and easy to dismantle and reassemblecomprising a pair of joint bars each having broad faces shaped toconform to broad surfaces of the rails including at least major portionsof the surfaces underlying the rail heads and the upper surfaces of therail bases in the area of the rail joint, said broad faces carrying athermoplastic adhesive layer about 25-50 mils in thickness, whichadhesive is characterized by:a. modulus in tension of at least 200,000psi at all temperatures from -20°F to 120°F, b. tensile strength of atleast 3000 psi at all temperatures from -20°F to 120°F, c. sufficientlylow softening point that it wets steel at 250°-300°F under moderatepressure, d. shear adhesion to cold rolled steel of at least 3000 psi atall temperatures from -20°F to 120°F, and e. water absorption of lessthan 1 percent after 24-hour immersion.